From a brief discussion on KarpAcrossAmerica.com.

The terms pop, soda, Coke, and other names for carbonated beverages are a source of great conflict among people of different regions. Soft drink is arguably the most neutral and politically correct term for these beverages, particularly because it fits into a nice beverage trifecta:

1) The Soft Drink
2) The Mixed Drink
3) The Hard Drink

With these three drink types, we can define some basic mixing relations (assume addition is commutative):

Soft + Soft == Soft
Soft + Mixed == Mixed
Soft + Hard == Mixed
Mixed + Mixed == Mixed
Mixed + Hard == Mixed
Hard + Hard == Hard

If a friendly game of Kings involves a community cup containing a Jack & Coke, wine, and water, the beverage can be expressed as: Soft + (Hard + (Hard + Soft)) = Soft + (Hard + Mixed) = Soft + Mixed = Mixed. For some reason, I think my 9th grade algebra teacher should be proud of this.